1. Field of the Invention
The present invention relates to a variable delivery compressor adapted mainly for use in a vehicular air-conditioning system.
2. Description of the Prior Art
As a vehicular air-conditioning system, there has been conceived a construction in which a compressor is run in an increased delivery state, when the temperature of a passenger's compartment is high as at an initial stage of the operation that a cooling load exerted upon the compressor is higher than the cooling capacity, but is run in a decreased delivery state when the compartment temperature drops to a point where the cooling load becomes lower than the cooling capacity. That variable delivery compressor is a swash plate type variable delivery compressor (as is disclosed in Japanese Patent Laid-Open No. 57-73877), which can alternately switch its delivery between 100% and 50%. Although not shown herein, a spool is axially movably mounted in the bore of a rear housing so that a delivery valve is pressed onto a valve plate by opening a first control valve to apply a delivery pressure to the back of the spool whereby the compression at the rear side is effective to perform a run of 100%, and so that the delivery valve is kept apart from the valve plate by closing the first control valve and opening a second control valve to apply a suction pressure to the back of the aforementioned spool whereby the compression at the rear side is made ineffective to switch the run to 50%.
As shown in FIG. 9 herein, the compressor described in the above has its delivery valve 57 constructed of a base portion 57a and reed portions 57b. When the delivery valve 57 slightly leaves a valve plate 4 in the decreased delivery state, as shown in FIG. 10, a refrigerant gas of a delivery chamber 20 flows into a shaft bore 4a (i.e., the suction system) so that the base portion 57a and the reed portions 57b are sucked toward the valve plate 4 until their leading ends strike eventually the valve plate 4. These strikes roughen the surface of the valve plate 4 such that shortage of sealing occurs sensing a drop in the volumetric efficiency in the run of 100% capacity in which the base portion 57a is intended to shut off the shaft bore 4a, as shown in FIG. 11. Especially in the case whether spool 44 vibrates in the axial direction when the aforementioned delivery valve 57 is attracted, the strikes become particularly intense so as to increase the wear of the valve plate 4 thereby to reduce the sealing efficiency.